Question 1

Which regex engine does this tester use?

Accepted Answer

It uses the native JavaScript RegExp engine in your browser. That means anything that works here will work identically inside Node.js, Deno, Bun, and any browser-based JavaScript runtime — and behavior matches the ECMAScript spec exactly.

Question 2

What flags are supported?

Accepted Answer

All six standard flags: g (global), i (ignoreCase), m (multiline), s (dotAll — . matches newlines), u (full Unicode), and y (sticky — match only at lastIndex). You can toggle any combination with one click.

Question 3

Does it support capture groups and named groups?

Accepted Answer

Yes. Each match shows numbered capture groups ($1, $2, …) and any named groups defined with the (?<name>…) syntax. This makes it easy to debug parsers and structured extractions.

Question 4

How are matches highlighted?

Accepted Answer

Matched substrings are highlighted inline in the test string view, so you can scan exactly which parts of your input are matched. The match list shows each result with its index for quick navigation.

Question 5

Why does it stop after 1000 matches?

Accepted Answer

For browser performance, the tester caps at 1000 matches per evaluation. If you hit that limit, refine your pattern (e.g. add anchors, narrow character classes) or split your input.

Question 6

Are my patterns private?

Accepted Answer

Yes — pattern compilation and matching run entirely in your browser. No input, pattern, or match output is sent to any server.

Regex Tester

Live Matching

Capture Groups

Common Presets

Frequently Asked Questions

What flavor of regex is this?

Can I use lookbehind?

How do I match newlines with .?

How do I write a Unicode-aware pattern?